Optical beam samplers are useful in a variety of applications where an energy of a beam of electromagnetic radiation needs to be determined. Typically, the energy needs to be determined for the purpose of control, compensation, and/or correction of variations in a power of a working beam without resulting in a significant reduction in the power of the working beam. Furthermore, a common requirement is to shape and homogenize the working beam of an optical system. The working beam is used for illumination of a specimen (or sample), for excitation of the specimen, and/or transmission through the specimen without preference to the rotational orientation of the working beam. The working beam is typically used without a need of further conditioning to remove variations in a cross-section intensity of the working beam.
Currently, a problem exists in using beam samplers of prior art where backscatter radiation, a result of an interaction of the working beam beyond the beam sampler, is reentrant to an output of the beam sampler and impinges upon a measuring means of the beam sampler. Due to single and/or multiple internal reflections within the beam sampler, backscatter is detected by the measuring means of the beam sampler, resulting in a sampling error of the working beam being greater than expected. To further detriment, measurement noise may be introduced into a measurement by interaction of the working beam with an object, such as a liquid surface, where instability in the liquid surface, due to vibration, movement, flow, etc., scatters energy inconsistently in direction and intensity. Instability in the backscattering surface is observed as measurement noise by the measuring means of the beam sampler. The problem is exasperated as additional optical surfaces are introduced into the optical system. For example, separate optics for field control of a radiation source, additional optics for shaping of the beam, and/or additional optics to correct astigmatism inherent in the radiating source. Based on currently available beam samplers, a removal of backscatter energy from impinging upon the measurement means is difficult and current beam samplers are prone to error in an assay of energy within the working beam.